BullardMcKenzie’s PhD supervisor, Edward Crisp Bullard (1907 – 1980), was a noted experimental physicist who devised innovative equipment and developed a dynamo theory to model the origin of the Earth’s magnetic field. He was a student of Ernest Rutherford and a pioneer of marine geophysics in the UK. He was head of the Department of Geodesy and Geophysics at Cambridge through the 1960s, noted as a good leader who supported his staff, always managing to find a little money to get a student to a significant conference or to kick-start a new project. suggested working on the thermodynamics of the lower mantle, relating the speeds of seismic waves to the pressure and temperature. McKenzie tackled this using state of the art equipment: painfully slow and noisy mechanical calculators. The project did not go well: “The technology was simply not there to do a proper job – it isn’t even there now.” But McKenzie’s work on the forces that govern the interactions of atoms at high pressure won him his Research Fellowship at King’s, after just 18 months as a graduate student – and with that came the freedom to follow his own interests.